BERLIN, March 29 (Reuters) - The co-pilot suspected of crashing a passenger jet in the Alps may have been suffering from a detached retina but investigators are unsure whether his vision problems had physical or psychological causes, a German newspaper said on Sunday.

Bild am Sonntag also reported how the captain of the Germanwings Airbus screamed "open the damn door!" to the co-pilot as he tried to get back into the locked cockpit before the jet crashed on Tuesday, killing all 150 aboard.

Another German newspaper, Welt am Sonntag, quoted a senior investigator as saying the 27-year-old co-pilot Andreas Lubitz "was treated by several neurologists and psychiatrists", adding that a number of medications had been found in his apartment in the German city of Duesseldorf.

Lufthansa, the parent company of the budget airline, said the carrier was unaware of a psychosomatic or any other illness affecting Lubitz. "We have no information of our own on that," a Lufthansa spokesman said.

A spokesman for state prosecutors in Duesseldorf declined to comment on Sunday on the various media reports, adding there would be no official statement before Monday.

The mass circulation Bild am Sonntag reported that investigators found evidence that Lubitz feared losing his eyesight apparently because of a detached retina. However, it was unclear whether this was due to an organic failure or psychosomatic illness, when physical problems are thought to be caused or aggravated by psychological factors such as stress.

Investigators have retrieved cockpit voice recordings from one of the A320 jet's "black boxes", which they say show Lubitz locked himself alone in the cockpit, before causing the jet to crash in southern France as it headed to Duesseldorf from Barcelona.

Mass circulation Bild am Sonntag reported that the voice recorder data showed that the locked-out captain said to his colleague inside the cockpit: "For God's sake, open the door."

The pilot can then be heard trying to smash the door down with a metal object. Even when he yells: "Open the damn door!" Lubitz does not give an answer as passengers' screams can be heard in the background just seconds before the fatal crash, the paper said.

The newspaper also reported that Lubitz's girlfriend, a teacher at a secondary school in a small town near Duesseldorf, recently told students that she was expecting a baby. (Reporting by Michael Nienaber; additional reporting by Tom Käckenhoff and Gernot Heller; editing by David Stamp)

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